hey Andres I did not know the definition of GHI: http://www.3tier.com/en/support/solar-prospecting-tools/what-global-horizontal-irradiance-solar-prospecting/ The radiation reaching the earth's surface can be represented in a number of different ways. Global Horizontal Irradiance (GHI) <http://www.3tier.com/en/support/glossary/#ghi> is the total amount of shortwave radiation received from above by a surface horizontal to the ground. This value is of particular interest to photovoltaic installations and includes both Direct Normal Irradiance (DNI) <http://www.3tier.com/en/support/glossary/#dni> and Diffuse Horizontal Irradiance (DIF) <http://www.3tier.com/en/support/glossary/#dif>.
irradiance=incoming solar radiation Landsat radiance=reflected solar radiation It looks from the definition of GHI that solar farming needs r.sun to answer to your question, - steradian (sr) is a "solid angle" of conic form, to which a circle applies for a plan projected footprint. - micro-meter (µm) is a spectrum value for the middle of the Landsat band used. Cheers, Yann On Wed, Jun 17, 2015 at 10:18 PM Andrés Oswaldo Calderón Romero < [email protected]> wrote: > Hello list, > > We are working in a solar energy project to locate potential sites for > solar panel farms. We are using the Landsat 7 panchromatic band to derive > radiance with i.landsat.toar (W/m2*sr*µm units). Now, we have access to > some ground data from sensors measuring global horizontal irradiance (GHI) > which output is in W/m2 units. I would like to compare these datasets for > validation, so, my question is rather simple: ¿Is there a way to convert > radiance in W/m2*sr*µm to irradiance in W/m2? > > I have read in [1] that radiance = irradiance / π, but I don't completely > understand, also, this doesn't take the spectral part (µm) into account. I > will very appreciate any further explanation about this... thank you very > much in advance!!! > > [1] http://earth.esa.int/landtraining07/D1LB3-Su.pdf > > -- > Atentamente, > > > *ANDRES OSWALDO CALDERON ROMERO* > M.Sc. Geoinformation Sciences & Earth Observation > Grupo de Investigación Aplicada en Sistemas - GRiAS > Universidad de Nariño > Pasto - Colombia > T: (+57) 301 382 9659 > > ------------------------------ > Correo Electrónico - Universidad de *Nariño* > Pasto - Nariño - Colombia > www.udenar.edu.co > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user
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